The murine and human cellular analogues of an avian retroviral transforming gene (c-myc) have been directly associated with chromosome translocations commonly observed in murine plasmacytomas (t(12;15)) and Burkitt lymphomas (t(8;14)). We propose to continue and extend our studies of the molecular basis and consequences of myc gene activation for cell transformation. Different molecular targets for myc rearrangements in murine plasmacytomas (PCTs) will be localized and their structures and significance for myc expression determined. To this end, we have recently identified a novel class of PCTs with translocation breakpoints clustered 5' of c-myc which alter the regulation of myc expression. The site of these translocations define the locations of putative regulatory elements important for normal c-myc gene control. The activities of c-myc promoter and potential enhancer elements will be assessed by their ability to drive the expression of a fused gene (i.e., chloramphenicol acetyl transferase or CAT) in fibroblasts and different lymphoid cell types. The chromatin structures of transcriptionally active and silent c-myc alleles will be compared to further characterize important regulatory regions. Modified myc genes will be stably integrated into lymphoid tumor cells which express either normal or truncated myc RNAs. The resultant effect(s) on normal and cryptic myc promoter activities will be determined. The activity of transfected and endogenous myc genes will also be compared in these transfected cells with myc exon and intron specific probes. These experiments will allow us to investigate potential cis or trans systems for regulating myc expression. The contributions of transcriptional and post-transcriptional mechanisms for c-myc expression will be assessed in a variety of lymphoid tumor lines bearing translocations which disrupt the c-myc locus. Finally, murine retroviral vectors containing either activated myc or human ras oncogenes will be introduced into normal proliferating B cells and their effects on growth factor dependency analyzed. (X)